Correlation in intelligence of virtual twins, same-age unrelated siblings raised together from early infancy, drops to zero in adulhood; correlation in real twins is high, consistent with genetic roots

Fullerton Virtual Twin Project: Overview and 2019 Update. Nancy L. Segal & Francisca J. Niculae. Twin Research and Human Genetics, July 29 2019. https://doi.org/10.1017/thg.2019.40

Abstract: Virtual twins (VTs) are defined as same-age unrelated siblings raised together from early infancy. This special class of adoptive siblings replays the rearing situation of twins, absent genetic relatedness. The first such pair was identified and studied in 1990 at the University of Minnesota, leading to the creation of the Fullerton Virtual Twin Study (FVTS) at California State University, Fullerton (CSUF) the following year. The registry currently includes 169 VT pairs, mostly children, with new pairs identified on a regular basis. These sibling sets provide a direct estimate of environmental influences on developmental traits and, as such, offer informative comparisons with ordinary monozygotic and dizygotic twins, full siblings and adoptive brothers and sisters. The sample characteristics, assessment battery and findings to date are summarized in this 2019 update.

---
Correlation in intelligence of virtual twins, same-age unrelated siblings raised together from early infancy, drops to zero in adulhood; correlation in real twins is high, consistent with genetic roots